In copending application U.S. Ser. No. 188,224 filed Sept. 17, 1980 allowed, there are disclosed novel block copolymers compositions comprised of acrylonitrile sequences and sequences of glutarimide units of a molecular weight of from about 10,000 to about 2,000,000 where the acrylonitrile sequences and sequences including glutarimide units are of a molecular weight of at least about 400 with the number of sequences being at least about 2 and preferably 5 and higher. The resulting block copolymers are relatively stable with regard to acids even at elected temperatures, but are reactive to basic materials.